Alloy for heat and corrosion resisting coating



Patented Dec. 9, 1952 UNITED STATES PTEN'E' OFFICE ALLOY FOR HEAT AND CORROSION RESISTING COATING No Drawing. Application October 7, 1947, Serial No. 778,466. In Great Britain October 9, 1946 2 Claims.

This invention is concerned with engineering parts which are exposed to stress and corrosion, particularly at high temperatures, e. g. 700 to 1000 C. Examples of such parts are the exhaust valves of internal combustion engines, blades, or other parts of internal combustion turbines and some steam stop-valves also stop valves and valves to handle sea water and for dies for casting or forging.

This invention has for one of its objects to provide protection for metal parts exposed to stress and/or corrosion, more especially at high temperature, by covering the surface of such part with a firmly adhering metal coating of higher resistivity than the part proper so protected.

The protective coating provided according to this invention is composed of a nickel-chromium alloy containing a comparatively high percentage of aluminum, some molybdenum, and some cobalt.

According to this invention we form an alloy of the following elements in the following amounts all being percentages by weight of the whole alloy:

Per cent Aluminium 7.5 to 13.5 Chromium 9.0 to 25.0 Molybdenum 0.1 to 5.0 Cobalt 0.1 to 1.0

Remainder nickel.

The molybdenum may be replaced in whole or in part by tungsten.

The following elements may be present:

Per cent Carbon Up to 0.35 Manganese Up to 2.0 silicon Up to 1.0 Iron Up to 1.0

The preferred range is as follows:

Per cent Aluminium 9.5 to 12.0 Chromium 10 to 11 Molybdenum 1.5 to 3.5 Cobalt 0.1 to 0.7 Carbon 0.05 to 0.15 Manganese 0.05 to 0.5 Silicon 0.1 to 0.3 Iron 0.0 to 1.0

Nickel the remainder.

Carbon is present as an impurity in most commercial materials and we prefer to keep it within the stated limits.

Silicon and manganese are added mainly as cleansing elements; also a small amount is 2 preferable for welding purposes. Excess, particularly of silicon, tends to decrease the anticorrosion properties.

Iron occurs as an impurity in many of the commercial metals used. It is definitely detrimental to corrosion resistance and while we prefer to keep it as low as possible it is dimcult entirely to eliminate.

One or more of the following elements may be added for cleaning or deoxidising purposes up to 0.5 per cent in total namely: calcium, magnesium, barium, boron, strontium and zinc, cerium and the other rare earth elements or misch-metal which act as grain controllers. Small residual amounts of calcium and/or cerium are particularly advantageous.

One or more of the following elements may be included as additional hardeners up to a maximum of 1 per cent of each and 2 per cent in total: titanium, vanadium, zirconium, tantalum, beryllium, niobium, silver, antimony and tin. Nitrogen may also be included up to 0.3 per cent.

The alloy may be heat treated to increase the hardness and strength. Suitable heat treatments are as follows: (1) ageing only at 500 to 800 C. (preferably at about 700 C.) for 8 to 16 hours, or (2) solution treatment at 1050 C. to 1250 C. for 2 to 8 hours followed by ageing as above.

Afterwards the part is cooled in air.

The solution treatment is not recommended 'for internal combustion engine valves as little advantage is gained and considerable damage may be done to the underlying steel or alloy. It is not necessary to age coated valves for use at temperatures around 500 to 850 C. but for parts which are to operate at temperatures below 500 or for parts which are to be used at lower, normal or room temperatures it may be advisable to age as required for a given hardness.

The coating is applied by welding or by any other known method.

The preferred process is to cast the alloy into 3 In order to apply the alloy to the base material of the valve or other part it is found that a flux is usually necessary.

One flux which is suitable is as follows:

Per cent Boric anhydride 40 to 45 Silica 12 to 15 Fluorite 17 to 20 Lime 24 to 28 Iron oxide and other impurities up to about 0.5 per cent are also usually present in the flux.

The flux, in the form of a finely divided powder is thoroughly mixed, damped with water and a thin even coat applied to the welding rods (by a rag, sponge or brush) which should then be allowed to dry thoroughly and not be used immediately.

Slightly oxidising conditions are preferred during the welding operation, and a little additional dry flux should be available to the operator should it be desired.

During application great care should be taken to avoid excessive dilution and contamination of the alloy by the base material on which it is being welded and also to avoid entrapment of small particles of the slag which is formed.

The resultant coat can be machined and has been found to have excellent strength and hardness at elevated temperatures as well as being heat and corrosion resistant.

What we claim is:

1. An alloy consisting by weight of approximately 9.5% to 12% aluminium, 10% to 11% chromium, 1.5% to 3.5% molybdenum, 0.1% to 0.7% cobalt, carbon not exceeding approximately 0.15%, 0.05% to 0.5% manganese, 0.1% to 0.3% silicon, iron not exceeding approximately 1.0%,

4 and the balance essentially all nickel substan tially as hereinabove described.

2. An alloy consisting by weight of approximately 9.5% to 12% aluminium, 10% to 11% chromium, 1.5% to 3.5% molybdenum, 0.1% to 0.7% cobalt, up to 1.0% iron, and the balance essentially all nickel substantially as hereinabove described.

HAROLD ERNEST GRESHAM. MARCUS ALAN WHEELER. DOUGLAS WILSON HALL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,273,877 Kuehrich July 30, 1918 2,071,645 McNeil Feb. 23, 1937 2,113,667 Swift Apr. 12, 1938 2,159,048 Pfeil May 23, 1939 2,246,078 Rohn et al June 17, 1941 2,403,128 Scott et al 1 July 21, 1946 2,432,149 Grifliths Dec. 9, 1947 2,450,803 Johnson Oct. 5, 1948 2,570,193 Bieber et al Oct. 9, 1951 FOREIGN PATENTS Number Country Date 342,868 Great Britain Feb. 12, 1931 371,334 Great Britain Apr. 13, 1932 591,641 Germany Jan. 24, 1934 425,614 Great Britain Mar. 15, 1935 OTHER REFERENCES Bureau of Standards Circular No. 100, Nickel and Its Alloys, 2nd ed., revised May 9, 1924, pp. 9-13. Published by G. P. 0., Wash., D. C. 

1. AN ALLOY CONSISTING BY WEIGHT OF APPROXIMATELY 9.5% TO 12% ALUMINUM, 10% TO 11% CHROMIUM, 1.5% T 3.5% MOLYBDENUM, 0.1% TO 0.7% COBALT, CARBON NOT EXCEEDING APPROXIMATELY 0.15%, 0.05% TO 0.5% MANGANESE, 0.1% TO 0.3% SILICON, IRON NOT EXCEEDING APPROXIMATELY 1.0%, AND THE BALANCE ESSENTIALLY ALL NICKEL SUBSTANTIALLY AS HEREINABOVE DESCRIBED. 